Acoustic device



July 31,1928. 1,678,833

E. H. SMYTHE ACOUSTIC DEVICE Filed. Feb 24, 1 926 Patented 1928. I

'YPATEFNT OFFICE."

Enwrir n 's imrrnnjor EvAnsroN, rumors, ASSIGNOR T WESTERN ELECTRIC COM- rm,;mcoEromrEn, oENEwaroma-N. Y., A CORPORATION on NEW YORK. V

ACOUSTIC DEVICE.

Application filed February 24, 1926. Serial No. 90,297.

This relates to acoustic devices and more particularly-to loud speaking receivers employing largedirect act ng diaphragms.

The object of this invention 13 to provide a loud speaker which will faithfull and eflicientlyreproduce all sounds within the frequencyrange of importance 1n speech and music.

One feature of the invention is a loud speaker with a non-rigid, non-peripheral mounting for the diaphragm. This is accomplished primarily by supporting the large direct actingdiaphragm upon either a numberof-knife edge or round posts or upon short flexible reeds such as strips of metal, both supporting mediums being positioned intermediate the point at which the diaphragm is actuated and the periphery, leaving the diaphragm free and unrestrained 2 with respect to torsional vibrations about th points of support, and the diaphragm partly or wholly. free with respect to transverse and radial movements.

Another feature of the invention is the 25. arrangement for attaching the diaphragm when using knife edge supports to allow the desired flexibility for maximum sound projectionwhile supporting the diaphragm irmly in position with relation to the driv- 3() ing mechanism.

The proper amount offlexibility is obtained when using the reed support through the medium of the reed itself which is elastic and which is positioned at such an angle with respect to the dia hragm and supporting frame that the diap ragm is unrestrained with respect to torsional vibrations about the points of support and transverse and radial movements.

Another feature of this invention comprises a loud speaker structure comprising two more or less separate portions cooperat ing in the production and radiation of sound waves. The rear section of this structure may be attached to the base of the apparatus and serves in principle, as a cylinder for a frontportion which acts as a piston.

Additional features and advantages will be apparent from the following detailed description read in conjunction with the accompanying drawings in which:

Fig. 1 is a perspective view of one embodiment of the mvention with a portion of the diaphragm broken away to show the supporting system.

Figs. 3 and4. are detailed views showing the manner of attaching diaphragm to the knife edge supports.

Fig. 5 is a cross-section of a loud speaker showing the reed supporting structure.

Fig. 6 is a cross-section showing the two section structure.

Fig. 7 shows a modified form of the sup porting post 8 illustrated in Figs. 2, 3'and 4, the modification residing in having the bearing surface of the post rounded.

On a base .1 and upright 2 are mounted supporting brackets 3 and diaphragm actuating unit '4.- preferably of the balanced armature type shown in Patent 1,365,898 to H. C. Egerton January 18, 1921. In Figs. 1 and 2 there is shown a ring 5 supported by the brackets 3 upon which ring are riveted four radial arms 6. These arms are rigid and are preferably arranged parallel with the surface of a diaphragm 10 which comprises a conical and a frusto-conical member secured together to form an air chamber. Upon the arms 6 are mounted knife edge or rounded studs 8, which support the diaphragm. This diaphragm as shown is driven by a rod 11 connected to the armature of the power unit 4. A series of holes 7 at varying distances from the center of the mounting structure may if desired be provided in the arms 6 to adjust the knife edge posts to various positions of engagement with the diaphragm; The knife edge posts are provided with threaded shanks which pass through the holes 7 and which are held in place by nuts 9. The bearing surfaces of the contact posts may be madefi-ounded as shown in Fig. 7 so as to permit the diaphragm to have a rolling movement over the bearing surfaces during Vibration thereby allowing substantially free oscillations. Torsional vibrations originating at the point of actuation are free to emanate to the periphery of the cone without substantial restraint or damping effect.

Fig. 3 shows the screw method of attaching the diaphragm to the knife edge supports. The holes in the supports are knife edge.

threaded and screws 12 inserted after first passing through the diaphragm. Between the head of the screw and the diaphragm a felt or rubber washer 13 is placed to protect the diaphragm from tearing and to ermit free response to the free oscillations of the diaphragm.

Fig. 4 shows the string and bead method of fastening. In this case the knife edge posts are provided with longitudinal bores through which, and the diaphragm 10, a cord 14 is passed. A bead 15 is attached to the string and bears against the rounded The cord or string is held taut by any suitable method of fastening such as a spring or by clamping or cementing. Additional flexibility is provided in this case by the cord itself.

In Fig. 5 the flexible reed method of mounting a diaphragm similar to that shown in Fig. 2 is illustrated. The mounting structure in this method differs somewhat from the construction which has been described in that the reeds 18 which may be of any suitable material such as thin strips of metal or .of other light elastic material are attached directly to the support-' ing brackets 3. Furthermore these reeds are positioned in such a manner as to make an acute angle wlth the diaphragm, small portions of the ends near the diaphragm "mounting structure.

being bent to provide' attaching surfaces. The diaphragm is attached to these reeds by means of threaded pins passing through holes in the material of the cone and carrying clamping nuts .19 on their protruding ends or by rivets, cementing or otherwise. In this method of mouting, transverse and radial movements are allowed to take place in the diaphragm as well as torsional vibrations about the points of support while the diaphragm is held in proper position with respect to the actuating rod 11. In this manner of suspension there is no tendency for the cone to take the pyramidal form as might be the case when it possesses transverse rigidity at the points of support, especially if the amplitude of vibration becomes great. With the reed support the diaphragm is free to adapt itself to a position which will allow maximum sound projection since it is not substantially restrained in any manner.

Fig. 6 shows a modification of this flexble mounting, the difference primarily being in the construction of the cone itself. The front portion of -thecone 20- is separated from the rear portion 21 and this latter portion is firmly attached to the The reeds 22 are similar to the reeds 18, except at the point of mounting where the reeds may be bent to a less degree and their ends are turned away from instead of toward the apex of the diaphragm. In this mounting structure the rear section serves as a cylinder to the front section which could be likened to a piston. The front section 20 has all the flexibility necessary for it to vibrate w1thout substantial torsional, transverse or radial restraint.

In these various modifications shown, the peripheries of the diaphragms are not fixed but are permitted to vibrate freely in response to all actuating impulses. This type of mounting permits of a greater freedom from damping and therefore gives a higher efiiciency in the 1 transmission of audible sound waves. Torsional, transverse and radial restraint has been reduced to optimum conditions.

What is claimed is:

1. An acoustic device comprising a large, direct acting diaphragm, a support, means for attaching said diaphragm to said support at a plurality of points removed from the outer edge of said diaphragm so as to leave the outer edge of said diaphragm free and permit the diaphragm to execute torsional vibrations about said points of support.

2. In an acoustic device, a large, direct acting diaphragm, an actuating device attached to said diaphragm at a point in its surface and a supporting member having a plurality of points of attachment to said surface, a plurality of supporting members positioned intermediate the point of actuation and periphery of said diaphragm, and means engaging said members to hold said diaphragm in position with respect to said actu'atmg device.

5 In an acoustic device, a large direct acting diaphragm, an actuating element attached to said diaphragm at a point in its surface, and a plurality of supporting members non-rigidly attached to said diaphragm intermediate the point of actuation and periphery to allow said diaphragm to execute its torsional, transverse and radial vibratory movements.

6. In an acoustic device, a large direct acting conical diaphragm, flexible supporting means having engagement with said diaphragm intermediate the apex and periphery thereof, said supporting means comprising a plurality of thin flexible reeds, said means supporting said dia hragm and at the same time allowing free cm of vibratory movement therein.

7. In an acoustic device, a sound projecting structure comprising two individual sections of similar size and configuration, said sections being acoustically coupled, one of said sections being relatively fixed, and-an actuating device positioned between said sections and driving the other of said sections at a point in itssurface, said driven section being mounted upon flexible reeds intermediate its point of actuation and periphery.

8. In an acoustic device a large direct acting diaphragm, an actuating device attached to said diaphragm at a point in its surface, a rigid support and non-rigid connections between said diaphragm and said support, said connections being positioned intermediate the point of actuation of the diaphragm and its outer edge.

9. A loud speaker comprising a large direct acting sound radiator, a standard, an actuating device and a plurality of rigid arms mounted on said standard said device being connected to a point on the surface of said radiator, and non-rigid connecting means between said radiator and said arms, said connecting means bein positioned intermediate the point at whic said actuating device is connected to said radiator and the periphery of said radiator.

10. A. loud speaker comprising a standard, a diaphragm including a conical and a frusto-conical member joined together at their outer edges to form an air chamber, an actuating device mounted on said standard and connected to the apex of the conical memher, and a lurality of flexible joints between said aphragm and said standard,

said joints being positioned intermediate the laspex and the outer edge of said conical mem- 11. A loud speaker comprising a standard, a plurality of rigid arms mounted thereon, a sound radiator including two dished surfaces united at their outer edges to form an air chamber, one of said surfaces having a portion cut away to permit the flow of air in and out of said chamber, an actuating device mounted on said standard, positioned withinsaid air chamber and connected to a point on the surface of one of the dished members, yielding members engaging one of said dished members and positioned between the actuating point and the outer edge thereof, and means for attaching said flexible members to said rigid arms.

12. in an acoustic device, a. large direct acting diaphragm, an actuating element connected with said diaphragm at a point on its surface and a supporting member having a non-rigid. connection with said diaphragm at a oint intermediate the point of actuation an the periphery of said diaphragm.

13. in an acoustic device, a large direct acting diaphragm, an actuating element connected with said diaphragm at a point on its surface and supporting means having a non-rigid connection with said diaphragm at a plurality of points intermediate the point of actuation and the periphery ei said diaphragm.

In witness whereof, i hereunto subscribe my name this EZOth'day of February A, D,

H. SMYTM, 

